This invention relates generally to audio power amplifiers and more specifically to an audio power amplifier that provides voltage and current amplification without employing overall negative feedback and without employing negative feedback within the voltage gain stages.
Audio power amplification has traditionally been accomplished by designing circuits that employ negative feedback techniques to increase linearity of the output signal. While this approach produces an amplifier which exhibits low distortion when measurements are made using sine wave input signals, these same amplifiers produce audible amounts of Transient Intermodulation Distortion (TIM) when reproducing more complex musical waveforms. The result of TIM is dynamic compression and a great loss of inner detail in the sound. In order to reduce TIM, several manufacturers have designed low-feedback audio power amplifiers. Others have designed amplifiers which employ no overall negative feedback, while retaining local negative feedback because of insufficient linearity within the circuitry. While these techniques, as well as other similar techniques such as feedforward, have reduced TIM, they leave considerable room for improvement. The present design allows for considerally more reduction in TIM due to the total elimination of all forms of negative feedback in all but the final or voltage follower stage of the amplifier. This is possible due to the advanced, highly linear power MOSFET gain circuitry which employs distortion cancellation rather than negative feedback to maintain high linearity. The result is sound reproduction that contains much more inner detail and is considerably more dynamic and transparent than is possible using conventional audio power amplifiers.